The present invention has utility with any osmotically active component in a body fluid, even though the following description, for simplicity, is focused on the monitoring of glucose.
It is a great demand, especially for persons suffering from diabetiesto monitor their glucose level in the blood as to gain a better regulation of the disease. Because of this, a number of different so called glucose metering system have been developed. One differs between two systems--invasive and non-invasive systems. Of these systems, it is the non-invasive system which has gained greatest interest and is currently used by thousands of people all over the world. The system is in principle based on a chemical reaction between a drop of blood and an oxidase on a so-called blood-stip. In its simplest form the glucose value can be evaluated by the changed colour on the strip, but more advanced systems includes an electronic recorder which calculate the actual value and shows it in display in mmol/l or mg/l. Even though the system is simple to operate, it has a number of drawbacks. It needs a sample of blood and this requires that persons have to pinch a hole in their finger to obtain this. And because of this, only a limited number of tests can be taken during a day, and the system can thus not monitor the glucose level continuously.
As regards invasive glucose sensors, a number of systems have been suggested and tried, but none of these have succeeded or been developed for practical use. The systems varies from implantable sensors based upon chemical reactions between blood and an oxidase, nuclear magnetic resonance, infrared light emission etc.
The objective of the present invention is to present an invasive sensor, especially a glucose sensor which can be implanted subcutaneously in interstitial liquid and where the level of glucose can be continuously monitored by an electronic detector outside the skin and where the electronic detector will show the values on a display, store the values and calculate average values over time, have an alarm for high and low preset values and at last, being able to calculate the need for insulin related to the actual level of glucose in the body and where this feature can be used to trigger an external or implanted insulin pump which altogether will act as an artificial pancreas.
The principle for the sensor is based upon osmosis.
In its simplest form, osmosis is the transportation of fluids across a semipermeable membrane separating two solvents with different concentration of solutes. The energy generated by the fluid flux activates the recording mechanism which can be an oscillating circuit or other means to detect the flux of water across the membrane in the current design.
The use of osmotic energy in a drug delivery system is known and in use. Felix Theeuwes describes in Journal of Pharmaceutical Sciences, 64: No.12, December 1975 the theory and principles related to the elementary osmotic pump, whereby drugs are delivered by an osmotic process at a controlled rate. Control resides in the: (a) water permeation characteristics of semipermeable membrane surrounding the formulated agent, and (b) osmotic properties of the formulation.
The use of osmosis as driving means for drug delivery systems is otherwise described by:
Sandra Z. Kernyi and Staynley L. Hartgraves, Oremature Excess Release From the Alzet Osmotic Pump, Pharmacology Biochemistry & Behavior, 27: pp. 199-201, 1987. PA1 F. Theeuwes and S. I. Yum, Principles of the Design and Operation of Generic Osmotic Pumps for the Delivery of Semisolid or Liquid Drug Formulations, Annals of Biomedical Engineering, 4: 343-353, 1976. PA1 Y. Sun, H. Xue, S. Janes, S. E. Sherman and D. L. Song, The use of an Alzet Osmotic Pump as a "Carryable" External Infusion Pump for Small Animal Studies, Proceed. Intern. Symp. Control. Rel. Bioact. Mater,. 17 (1990), Controlled Release Society, Inc., 17: 384-371, 1990.
As can be seen the osmotic principle and the use of this principle in drug delivery systems are well known.